Thanks bro it should be like this
it can be solved by using the concept of combinatories,
We have condition a+b<=1001 so possible equations are as follows
a+b=2 since a>=1 and b>=1 modfied eq is a+b=0 total cases here 2-1+0C0 =1C0 =1
a+b=3 similarly here it is a+b=1 and total cases are 2-1+1C1 =2C1 =2
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a+b=1001 similarly here it is a+b=999 and total cases are 1000C999 =1000